PROJECT SUMMARY Attention-deficit/hyperactivity disorder (ADHD) is a chronic condition, present from early childhood, which persists throughout the lifecourse. There is now clear evidence that children entering kindergarten, that are relatively young for the grade (e.g., born in the months immediately preceding the school entry cut-off) are at significantly more risk for receiving an ADHD diagnosis and being prescribed stimulant medication. These risks appear to be related solely to age of entry when other explanatory variables are controlled (Elder, 2010). This situation, termed the ?Relative Age Effect? in this literature has potentially serious consequences for kindergarten children (e.g., greater likelihood of being prescribed psychoactive medication to control behavior; Elder, 2010). The present proposal aims to develop a teacher intervention to attenuate the impact of the relative age effect on young kindergarteners with elevated ADHD symptoms, and test the correspondence between the hypothesized mechanisms and treatment outcomes related to ADHD (e.g., symptoms, impairment). Following intervention development and refinement, 60 children entering kindergarten in the fall, and young for the grade, will be randomly assigned to (1) Kindergarten as Usual (KAU); (2) a Relative Age Effect prevention intervention administered immediately; or (3) a Relative Age Effect prevention intervention administered mid-year. In the intervention groups, teachers will be introduced to the relative age effect, receive information on how to anchor behavioral ratings in developmental norms, and implement a positive behavioral support to support growth in the child across the kindergarten school year. Primary aims will be to demonstrate the feasibility and acceptability of the intervention approach as well as the ability of the team to retain young children in a longitudinal trial. Further, the hypothesized mechanisms (e.g., improved neurocognitive functioning; improved teacher use of positive behavioral supports) will be measured and correspondence to hypothesized outcomes (e.g., reduced ADHD symptoms and impairment) will be evaluated. Data collected will be used to justify a larger efficacy-based trial to support the positive development of children with ADHD during this critical developmental transition.